An electric double layer capacitor or EDLC is a type of capacitor that typically consists of carbon electrodes (separated via a porous separator), current collectors and an electrolyte solution. When electric potential is applied to an EDLC cell, ionic current flows due to the attraction of anions to the positive electrode and cations to the negative electrode. Electric charge is stored at the interface between each polarized electrode and the electrolyte solution.
EDLC designs vary depending on application and can include, for example, standard jelly roll designs, prismatic designs, honeycomb designs, hybrid designs or other designs known in the art. The energy density and the specific power of an EDLC can be affected by the properties thereof, including the electrode and the electrolyte utilized. With respect to the electrode, high surface area carbons, carbon nanotubes and other forms of carbon and composites have been utilized in manufacturing such devices. Of these, carbon based electrodes are common and are widely used in commercially available devices.
Conventional carbons for such electrodes can be prepared from natural materials such as wood, charcoal and coal tar pitch, or from synthetic materials such as resins. Where synthetic precursors are utilized, the precursor is typically first crosslinked to solidify the precursor, carbonized in an inert atmosphere (such as nitrogen) and then activated. The activation is usually performed by heating the carbon at high temperatures (800-900° C.) in a partially oxidized atmosphere (such as carbon dioxide). During the carbonization/activation process, a large number of micropores are formed in the surface of the carbon material. Micropores increase the surface area of the carbon which results in increased capacitance. Other conventional carbons for electrodes may be formed from cured synthetic precursors that are treated with alkali or acids and then further treated at high temperatures to create porosity.
EDLC's incorporating carbon electrodes manufactured by such conventional processes heretofore usually have an energy density within the range of 6-7 Wh/l. However, this energy density range is not sufficient or practical for high energy applications, such as for hybrid vehicles. Accordingly, a new carbon material for use with EDLC's suited for high energy applications is needed.